I just wanted to document this error somewhere because it was not clear the root cause and I could not find anything on Google. When running
//$ hg svnclone http://jsonpickle.googlecode.com/svn/trunk/ jsonpickle-hg//
I received: // python: /build/buildd/subversion-1.5.1dfsg1/subversion/libsvn_subr/path.c:350: svn_path_remove_component: Assertion `is_canonical(path->data, path->len)' failed. Aborted//
Eventually I took the trailing slash off the URL and did not get any errors, but hgsubversion did not convert the repository (I got an empty repo):
//$ hg svnclone http://jsonpickle.googlecode.com/svn/trunk jsonpickle-hg2 0 files updated, 0 files merged, 0 files removed, 0 files unresolved//
Finally, I took the "trunk" off, and everything went smoothly: //$ hg svnclone http://jsonpickle.googlecode.com/svn jsonpickle-hg converting r1 by None ...//
It would be nice if the README and "Use" wiki page reflected this requirement. I have attached a patch that adds a sentence to the README file.